SQL is a database computer language designed for the retrieval and This reference has been prepared for the beginners to help them understand the basic to advanced concepts related to SQL languages. Prerequisites. Before you start doing practice with various types of examples given in this SQL Commands. Glossary of commonly used SQL commands. Codecademy is the easiest way to learn how to code. It's interactive, fun, and you can do it with your friends. Here are the most commonly used SQL commands and the most commonly used options for each. There are commands. Common MySQL Column Types. Purpose. Data Type. Example. Integers Basic MySQL Commands. What. How.
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again. Tins lesson also covers the use of SQL*Plus commands to execute . example on the slide, displays all columns and all rows of the DEPT table: SELECT. basic understanding of SQL and to get a feel of how it works. Audience on the various components of SQL along with suitable examples. . SQL Commands. Basic Retrieval Queries in SQL Main SQL command for data definition Assigned to column in any tuple for which a value is not specified. ▫ Example.
I have been sharing some free eBooks on different technologies e. Some of the books are available for free to read online others you can download in PDF format. In this example we will return the top 25 from our Customers table:. So far we have explored SQL query commands for querying tables and combining records from multiple queries. As an example, this next query fetches a list of customers by the region where there is at least one customer per region:
There is a tradeoff when naming columns to make them succinct results in reduced readability in subsequent daily use. In our Orders table, the item column contains the description of purchased products. In the following example, we will return records from the Orders table where the idea is to get a list of high volume orders for a given item, in this case for customers who ordered more than 50 of the product:.
Here we can simply add the comment delimiter to deactivate it momentarily:.
So far we have explored SQL query commands for querying tables and combining records from multiple queries. Here, we are going to create the DB as a container for our Customers and Orders tables used in the previous ten examples above:. Although most databases are created using a UI such as Access or OpenOffice, it is important to know how to create and delete databases and tables programmatically via code with SQL statements.
This is especially so when installing a new web app and the UI asks new users to enter names for DBs to be added during installation. Imagine that you decide to send a birthday card to your customers to show your appreciation for their business, and so you want to add a birthday field to the Customers table.
Accurate indexing requires that the Primary Key column contain only unique values for this purpose. This guarantees that JOIN statements will maintain integrity and produce valid matches. We can extend the functionality of the Primary Key so that it automatically increments from a base.
For example:. Performance pitfalls can be avoided in many ways.
We advise developers to learn SQL server queries to an advanced level for this purpose. For production purposes, these tips may be crucial to adequate performance. Have a look at this query with a subquery condition:.
There are a hundred and one uses for this SQL tool. Suppose you want to archive your yearly Orders table into a larger archive table. This next example shows how to do it. As an example, this next query fetches a list of customers by the region where there is at least one customer per region:.
Substring is probably the most valuable of all built-in functions. Suppose you want to find the substring left of the dots in a web address. PDF captures formatted documents such as images, React Native revolutionized the way mobile apps were developed, largely because of its use of native code components. Components are complete units of code meant Tables; 2. Query for Creating a View A view is a tailored table that is formed as a result of a query.
Query for Retrieving a View The standard syntax of selecting attributes from a table is applicable to views as well.
Query to Display User Tables A user-defined table is a representation of defined information in a table, and they can be used as arguments for procedures or user-defined functions. Query to Display Primary Keys A primary key uniquely identifies all values within a table.
Displaying Foreign Keys Foreign keys link one table to another — they are attributes in one table which refer to the primary key of another table.
Displaying Internal Tables Internal tables are formed as a by-product of a user-action and are usually not accessible. Displaying a List of Procedures A stored procedure is a group of SQL queries that logically form a single unit and perform a particular task. Thus, using the following query you can keep track of them: Swapping the Values of Two Columns in a table In this and subsequent examples, we will use a common company database including several tables which are easily visualized. We can easily fix this problem with the following SQL statement: Returning a Column of Unique Values Now, suppose that our data entry operator added the same Customers to the Customers table more than once by mistake.
In this example we will return the top 25 from our Customers table: Between Monday and Tuesday Today is Wednesday, and we arrive at work and discover that our new data entry clerk in training has entered all new orders incorrectly on Monday and Tuesday.
The Between clause makes the task a breeze: Finding the Intersection of Two Tables Undoubtedly the whole reason that a relational database exists in the first place is to find matching records in two tables!
Here we are going to fetch a list of all records which have matches in the Customers and Orders tables: Here is a quick way to accomplish the task: Making Column Labels More Friendly Aliasing column labels give us the convenience of renaming a column label to something more readable. Use the Index, Luke!
Markus Winand Download: This book is for developers; it avoids unnecessary details about database internals. That's all in this list of Free SQL books for beginners and experienced developers. You can download these books as free PDF or read them online as well.
Even if you know SQL and have been using it for few years, you will be amazed to learn many new things in some of these books, especially the first two books are great for experienced SQL programmers, I just loved them when I found first and has since read them many times already.
If you have any question or you know a good SQL book which is available for free and wants to add to this list then please feel free to drop a note. Posted by javin paul Email This BlogThis!
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